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Mainly temperature dependant. I've not been able to show much sensitivity to light yet (indoors).Originally Posted by rore85
Yes, the pressure reading is very 'active' so I used the maximum OSS and then 10x averaging as well. It could do with even more...
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The complete opus in Longs
Here it is. This works, and give you a corrected temperature and pressure reading from a Bosch BMP085 barometric pressure sensor.
It requires a PIC18FXXXX MCU and use of PBPL compiler option. You'll need to change the configs for whatever PIC you choose and change the Serout2 statements to LCDOUT or whatever you want to display data on.
The main point of this post is really to show the calculations and variable casting and manipulation required.
Code:'****************************************************************************** 'MR.SNEEZY - test code for FrSky using Bosch BMP085 baro sensor. 'This version is for PIC 18F4620 ' 'ADD/Do ' 'NOTES - ' 'LAST ACTION - scratch my head... ' 'PIC 18F1220 port/pin alocations '-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- 'PortA.0/Pin 2 = Serial TX 'PortA.1/Pin 3 = LED 'PortB.0/Pin 33 = I2C SCL clock 'PortB.1/Pin 34 = I2C SDA data ' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- 'Config Directive settings for MPASM (fuses) for 18F4620 @ __CONFIG _CONFIG1H, _IESO_OFF_1H & _FCMEN_OFF_1H & _OSC_INTIO7_1H @ __CONFIG _CONFIG2L, _PWRT_ON_2L & _BOREN_OFF_2L @ __CONFIG _CONFIG2H, _WDT_OFF_2H & _WDTPS_512_2H @ __CONFIG _CONFIG3H, _MCLRE_OFF_3H & _PBADEN_OFF_3H @ __CONFIG _CONFIG4L, _DEBUG_OFF_4L & _LVP_OFF_4L & _STVREN_OFF_4L & _XINST_OFF_4L @ __CONFIG _CONFIG5L, _CP0_OFF_5L & _CP1_OFF_5L & _CP2_OFF_5L & _CP3_OFF_5L @ __CONFIG _CONFIG5H, _CPB_OFF_5H & _CPD_OFF_5H @ __CONFIG _CONFIG6L, _WRT0_OFF_6L & _WRT1_OFF_6L & _WRT2_OFF_6L & _WRT3_OFF_6L @ __CONFIG _CONFIG6H, _WRTC_OFF_6H & _WRTB_OFF_6H & _WRTD_OFF_6H @ __CONFIG _CONFIG7L, _EBTR0_OFF_7L & _EBTR1_OFF_7L & _EBTR2_OFF_7L & _EBTR3_OFF_7L @ __CONFIG _CONFIG7H, _EBTRB_OFF_7H DEFINE OSC 8 '8Mhz clock used. ' Define some constants if needed ' Software Defines (variables and pins) Cal_table var word[11] '11 word array to store calibration data lUpres var long 'Long variable for Uncompensated Pressure lPres var Long 'Long variable for Compensated Pressure lTemp_Var1 Var long 'Long temporary variable X1 var Long X2 var Long X3 var Long B3 var long B4 var long B5 var long B6 var Long B7 var long lAC1 var Long 'Long variables for cal values actually negative in my sensor lAC2 var long 'These are 'cast' from the Word vars into Long vars in code below lAC3 var Long lAC4 var Long lMB var Long lMC var Long bTemp_Var1 var byte 'Byte temp variable wTemp_Var1 var Word 'Word temp variable wTemp_Var2 var word 'Word temp variable lUTemp var long 'Uncompensated temperature reading from sensor lCTemp var Long 'Compensated (real) temperature x10 (1/10th of C) from sensor i2c_Reg var Byte 'variable for target i2c register address CPIN var PortB.0 ' I2C clock pin DPIN var PortB.1 ' I2C data pin SO Var PortA.0 'Serial out pin LED var PortA.1 'Indicator LED, via 500ohm to +3.3V OSS con $3 'This value is the Over Sampling Setting for the BMP085 '0 = minimum, 3 = maximum. Also change value in Read_pres if you alter OSS 'Alias's for calibration data in the sensor to match the Bosch parameter list names AC1 var Cal_table[0] ' AC2 var Cal_table[1] 'BMP085 has 11 16bit values stored in EEPROM AC3 var Cal_table[2] 'First byte is at $AA last at $BF, two bytes per cal value AC4 var Cal_table[3] 'Lowbyte is MSB (e.g $AA), Highbyte is LSB (e.g. $AB) AC5 var Cal_table[4] ' AC6 var Cal_table[5] B1 var Cal_table[6] 'Warning - AC4, AC5, AC6 are UNSIGNED values, the rest are SIGNED B2 var Cal_table[7] MB var Cal_table[8] MC var Cal_table[9] MD var Cal_table[10] ' Initialise Processor - check for each PIC type ' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ADCON1 = %00001111 'Turn off all AD's ' OSCCON = %01100111 'set INTRC to 4 MHZ OSCCON = %01110111 'set INTRC to 8 MHZ ' OSCTUNE = 0 'OSC trim set to Null ' Set initial state of port pins as Input or Output if needed ' TRISA = %11111100 'Input(0 = output, 1 = Input) ' TRISB = %11111100 ' ' TRISC = %11111111 ' TRISD = %11111110 ' TRISE = %11111111 ' PIC initialization code ' Low So 'Start low, or you get rubbish on the LCD at PIC boot up. Gosub Alive 'Go prove the PIC is running via LED Serout2 SO,16780,[$FE,$01] ' Clear LCD & home LCD cursor. pause 10 ' wait for LCD to catch up Serout2 SO,16780,[" FrSky Vario "] ' Serial print Serout2 SO,16780,[$FE,$C0] ' Shift cursor to line2 Serout2 SO,16780,[" Development Jig "] ' Serial print Pause 2000 i2c_Reg =$AA 'Start address of the BMP085 calibration data I2CREAD DPIN,CPIN,$EF,I2C_REG,[STR Cal_table\11],cal_error 'Read 11 reversed words out of sensor AC1 = (AC1.lowbyte<<8) + AC1.highbyte 'swap MSB and LSB of each to use in PBP (un-reverse then) AC2 = (AC2.lowbyte<<8) + AC2.highbyte 'device stores the MSB in the Low byte, LSB in the High byte AC3 = (AC3.lowbyte<<8) + AC3.highbyte AC4 = (AC4.lowbyte<<8) + AC4.highbyte AC5 = (AC5.lowbyte<<8) + AC5.highbyte AC6 = (AC6.lowbyte<<8) + AC6.highbyte B1 = (B1.lowbyte<<8) + B1.highbyte B2 = (B2.lowbyte<<8) + B2.highbyte MB = (MB.lowbyte<<8) + MB.highbyte MC = (MC.lowbyte<<8) + MC.highbyte MD = (MD.lowbyte<<8) + MD.highbyte 'Cast (convert) signed PBP Word vars to signed PBP Long vars where needed by math routines below lAC1 = AC1 'copy word to long if AC1.15 then lAC1.HIGHWORD = $FFFF 'Check for negative, set top 16bits to all 1's if true lAC2 = AC2 'copy word to long if AC2.15 then lAC2.HIGHWORD = $FFFF 'Check for negative, set top 16bits to all 1's if true lAC3 = AC3 'copy word to long if AC3.15 then lAC3.HIGHWORD = $FFFF 'Check for negative, set top 16bits to all 1's if true lMB = MB 'copy word to long if MB.15 then lMB.HIGHWORD = $FFFF 'Check for negative, set top 16bits to all 1's if true lMC = MC 'copy word to long if MC.15 then lMC.HIGHWORD = $FFFF 'Check for negative, set top 16bits to all 1's if true 'Cast (convert) UN-signed PBP Word var to UN-signed PBP Long var for math routines below lAC4 = AC4 'copy word to long, both unsigned Serout2 SO,16780,[$FE,$01] ' Clear LCD & home LCD cursor. Pause 10 ' wait for LCD to catch up 'Main loop -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Main: Serout2 SO,16780,[$FE,$02] 'home LCD cursor, LCD not cleared. Gosub Read_temp 'get Temp via I2C Serout2 SO,16780,["UT=",SDEC lUtemp," "] 'Send Word size number to LCD lTemp_Var1 = 0 'Clear the last pressure reading For bTemp_Var1 = 0 to 9 'Start of 10x averaging routine Gosub Read_pres 'get Long uncompensated pressure via I2C lTemp_Var1 = lTemp_Var1 + lUpres Next bTemp_Var1 lUpres = lTemp_Var1 / 10 'finish of the 10x Averaging routine Serout2 SO,16780,["UP=",SDEC lUpres," "] 'Send Word size number to LCD 'Calculate temperature in 1/10ths of Deg C from lUTemp ' Note 2^15 = 32768 Dec or $8000 X1 = ((lUtemp - AC6) * AC5) / $8000 'find X1. X2 = (lMC * $800) / (X1 + MD) 'Find X2. Note:- math rounding results in X2 being in error by 1 ? B5 = X1 + X2 'Find B5 from X1 and X2. lCTemp = (B5 + 8) / 16 'Hey presto, lCTemp appears... 'DISPLAY true temperature in C X1 = lCTemp / 10 'find value above decimal point Serout2 SO,16780,[$FE,$C0] ' Shift cursor to line_2 Serout2 SO,16780,["Temp= ",DEC X1,"."] 'Send Word size number to LCD X1 = lCTemp // 10 'Find decimal value Serout2 SO,16780,[DEC X1," "] 'Send Word size number to LCD 'Calculate pressure in Pascals from uncompensated pressure lUpres (1/100th's of hPa's) B6 = b5 - 4000 x1 = (b2 * (B6 * B6 / $1000)) / $800 x2 = (lac2 * B6) / $800 x3 = x1 + x2 B3 = ((lac1 * 4 + x3) << OSS + 2) / 4 'OSS = Over Sampling constant set above x1 = (lac3 * b6) / $2000 x2 = (b1 * (b6 * b6 / $1000)) / $10000 x3 = ((x1 + x2) + 2) / 4 B4 = (lac4 * (x3 + 32768)) / $8000 'Find B4, note lAC4 is an unsigned Long B7 = (lUPres - B3) * (50000 >> OSS) 'OSS = Over Sampling constant set above If B7 < $80000000 then 'branch if value is above or below range lPres = (B7 * 2) / B4 Else lPres = (B7 / B4) * 2 Endif X1 = (lPres / 256) * (lPres / 256) X1 = (X1 * 3038) / $10000 '$10000 = 2^16 X2 = (-7357 * lPres) / $10000 lPres = lPres + (X1 + X2 + 3791) / 16 'lPres is the true pressure in Pa 'DISPLAY true pressure in hPa X1 = lPres / 100 'find value above decimal point Serout2 SO,16780,[$FE,$94] 'Shift cursor to line_3 Serout2 SO,16780,["hPa= ",DEC X1,"."] 'Send Word size number to LCD X1 = lPres // 100 'find value below decimal point Serout2 SO,16780,[DEC X1," "] 'Send Word size number to LCD pause 1000 Toggle LED 'flash the 'im alive' LED Goto main 'SUBROUTINES -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Read_pres: i2c_Reg = $F4 '$F4 is the control register address I2CWRITE DPIN,CPIN,$EE,I2C_REG,[$F4] ' Write $34+(oss << 6) to set pressure conversion Pause 30 ' Delay 10ms after each write (30mS for HiRes results (oss=3)) i2c_Reg = $F6 '$F6 is the result register MSB I2CREAD DPIN,CPIN,$EF,I2C_REG,[lUpres],I2C_error 'Read pressure MSB, LSB, XLSB, $F9 ($F9 not actually wanted). lUpres = lUpres >> (16 - oss) 'remove $F9 from result (>>8), and left shift result back to 16 to 19 Bits (OSS value dependant) 'it's because PBP reads four bytes if [Var] is a long... return 'we only want top 19bits of the result. Read_temp: i2c_Reg = $F4 '$F4 is the control register address I2CWRITE DPIN,CPIN,$EE,I2C_REG,[$2E] ' Write $2E to set temperature conversion Pause 10 ' Delay 10ms after each write i2c_Reg = $F6 '$F6 is the result register MSB I2CREAD DPIN,CPIN,$EF,I2C_REG,[wTemp_Var1],I2C_error 'Read temperature MSB, LSB. lUTemp = wTemp_Var1 'copy word to long. Note BMP085 UT is NOT a signed value return 'Prove it's alive Alive: High LED 'flash LED routine For btemp_var1 = 10 to 110 step 10 Low LED Pause bTemp_Var1 High LED Pause bTemp_Var1 Next bTemp_Var1 Return 'trap and display I2C problems I2C_error: Serout2 SO,16780,[$FE,$01] ' Clear LCD & home LCD cursor. Pause 10 ' wait for LCD to catch up Serout2 SO,16780,["i2c bus read error"] 'no ACK from I2C device pause 2000 Toggle LED Goto main Cal_error: Serout2 SO,16780,[$FE,$01] ' Clear LCD & home LCD cursor. Pause 10 Serout2 SO,16780,["i2c cal read error "] ' End
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